1. Field of the Invention
The present invention relates to a master cylinder for braking in which a sub-tank for supplying working oil for braking is integrally provided on a master cylinder main body, and a method of making a master cylinder.
2. Background Art
A disk-type brake system is known a four-wheeled car, motorcycle, or motor-tricycle, in which a sub-tank for supplying working oil for braking is integral with a master cylinder for feeding the working oil to a caliper (see Japanese Utility Model No. Hei 3-2962, and Japanese Patent Laid-open No. Hei 10-236374).
In the master cylinder, two ports close to each other in a partition wall for partitioning the sub-tank from a master cylinder main body.
To easily form these ports by machining, the sub-tank has a large opening extending substantially over the entire length of the master cylinder main body, and a lid having a large area is mounted to cover the opening.
Since the prior art master cylinder for braking integrated with the sub-tank is configured as described above, master cylinder is large. Because a lid having a large area must be liquid-tightly mounted to cover the opening of the sub-tank, the tightly sealing structure must cover a large area, increasing cost.
An object of the present invention is to solve the above-described problem of the prior art master cylinder for braking integrated with a sub-tank, and to provide a master cylinder for braking of reduced size, complexity, and difficulty of manufacture.
The present invention satisfies the above goals and other advantages not contemplated by conventional devices. A master cylinder for braking includes a sub-tank for supplying working oil for braking integral with a master cylinder main body. A first port and a second port are formed close to each other in a partition wall for partitioning the master cylinder main body from the sub-tank so as to pass through the partition wall.
The sub-tank has a first opening and a second opening. The first opening is located at a position through which the axis of the first port and the axis of the second port pass, and the second opening is located at the highest position of the sub-tank. The working oil for braking is supplied in the sub-tank through the second opening.
As a result of the above configuration, the first and second ports can be formed by a tool inserted through the first opening, and the size of the first opening can be made relatively small. This reduces the size of the master cylinder. The seal structure can also be reduced in size and simplified, increasing the reliability of the seal. In turn this reduces difficulty of manufacture and cost.
Further, the second opening is located at the highest position (upper portion) of the sub-tank, and the working oil for braking is supplied in the sub-tank through the second opening.
As a result, because working oil for braking can be supplied at a position near the master cylinder main body for braking, it is possible to supply the working oil while checking the charging state of the working oil to the master cylinder, and hence to facilitate the supply of the working oil.
Because the port for supplying working oil for braking is directly formed in the upper end wall of the sub-tank, the number of parts necessary for supply of the working oil is minimized, and thereby the structure of the supply port can be simplified. This makes it possible to further reduce the size of the master cylinder for braking. In addition, the axis of the first port may cross the axis of the second port.
As a result, the size of the first opening can be further reduced, further reducing the size of the master cylinder for braking and the seal structure and increasing the reliability of the seal structure.
Because the axis of the first port crosses the axis of the second port (when viewed from the side), it is easy to form the two ports close to one another without impairing the strength of the partition wall.
The first opening may be provided with a window for checking a residual amount of the working oil for braking. The window can be formed by making use of the first opening provided for forming the first and second ports by machining. In other words, the first opening serves as structure for the window. As a result, it is possible to further simplify the structure of the master cylinder for braking.
The sub-tank may have a third opening at a position between the first opening and the second opening. The third opening is provided with a window for checking the residual amount of the working oil for braking.
The shape of the window provided for the third opening formed in the sub-tank can be freely selected, facilitating checking of the residual amount of working oil for braking.
The master cylinder having a sub-tank integral with a master cylinder main body may include a communication port for communicating the master cylinder main body to the sub-tank formed in the partition wall. The communication port may be formed via an opening for machining formed in a wall surface of the sub-tank, and the opening for machining blocked after formation of the communication port.
Because the opening for machining is blocked after formation of the communication port, a special seal member for the opening for machining is not required. This reduces the size of the master cylinder.
It is desirable to keep the opening for machining as small as possible, while still allowing a tool for forming the communication port to pass the opening for machining. The opening for machining is formed in a wall surface, facing to the other wall surface on the master cylinder main body side of the sub-tank. In this configuration, it is possible to easily form the communication port by machining.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.